An advanced practice nurse must teach a diabetic patient who has been started on an intensive insulin therapy regimen how to determine the proper dose of insulin to use before a meal. The patient will be on a regimen of Lantus 20 units at bedtime and Novolog 5 units before each meal. Before meeting with the patient, the nurse must review the patient's records for several factors needed to perform the dosage calculations.

First, the nurse must know the patient's "average" Total Daily Dose (TDD), the total amount of long-acting and rapid-acting insulin used in a single day.

• The patient's regimen of 20 units of Lantus and 5 units of Novolog before each meal produces a TDD of 35 units.

Second, the nurse must calculate the patient's Insulin Sensitivity Factor, also called the Correction Factor. The Insulin Sensitivity Factor is a measure of the lowering effect of 1 unit of insulin on the blood glucose (BG) level in milligrams/deciliter (mg/dl), and it is determined using the "1,800 rule": 1,800 divided by TDD.

After rounding 51.4 mg/dl to the nearest unit, the nurse will know that 1 unit of insulin will lower the blood glucose (BG) by 51 mg/dl.

Third, the nurse must calculate the Insulin to CHO (Carbohydrate) Ratio. The Insulin to CHO Ratio indicates how many grams (gms) of carbohydrate will be offset by 1 unit of insulin. It is determined using the "500 rule": 500 divided by TDD.

After rounding 14.3 gms to the nearest unit, the nurse will know that the patient will need an additional unit of Novolog for every 14 grams of carbohydrate consumed (a 1:14 ratio).

With this information and the blood glucose goal of 120 mg/dl, the nurse teaches the patient to use two formulas to calculate insulin dosages needed before each meal.

The first formula involves the patient's actual blood glucose before the meal (BG), the blood glucose goal of 120 mg/dl (Y) and the insulin sensitivity or correction factor (X). For instance, before lunch, the patient takes a blood glucose reading of 280 mg/dl:

The second formula involves the number of grams of carbohydrate in the patient's lunch and the number of insulin units needed. For instance, the patient's lunch will contain 45 gms of CHO. Using the Insulin to CHO Ratio:

The combination of these two results means that the patient will need a dose of 6 units of Novolog before this particular lunch.

The formulas are used as a guide and may be modified based on patient history. For example, if the patient has frequent hypoglycemia and the nurse's review of patient records indicates that the Insulin Sensitivity Factor of 51 will not be safe, the nurse may round it up to 55 or 60.